This invention relates to 3-anilinopyrazolone magenta dye-forming couplers having a particular parent group and thio coupling-off group that enables improved photographic properties and to photographic materials and processes comprising such couplers.
In color photographic silver halide materials and processes so-called four equivalent 3-anilino pyrazolone couplers have provided magenta dye images having useful properties. Examples of such compounds are described in, for example, U.S. Pat. No. 3,907,571, U.S. Pat. No. 3,928,044, U.S. Pat. No. 3,935,015, U.S. Pat. No. 4,199,361 and U.S. Pat. No. 3,519,429. An example of one such pyrazolone coupler, described in, for example, U.S. Pat. No. 3,519,429 is herein designated as comparison coupler C-1 and is represented by the formula: ##STR1## This prior art coupler has a number of disadvantages. Since C-1 is a four-equivalent coupler, more silver halide and coupler must be used to obtain adequate dye yield, when compared to two-equivalent couplers. This increases the costs associated with this type of coupler. In addition, the dye dark stability is quite poor and the coupler itself causes substantial yellow stain in areas of minimum density, especially when kept under humid conditions.
In color photographic silver halide materials and processes, pyrazolone couplers comprising arylthio coupling-off groups have provided magenta dye images having useful properties. Examples of such compounds are described in, for example, U.S. Pat. No. 4,413,054, Japanese published patent application 60/057839, U.S. Pat. No. 4,876,182, U.S. Pat. No. 4,900,657 and U.S. Pat. No. 4,351,897. An example of such a pyrazolone coupler described in, for example, U.S. Pat. No. 4,413,054 is designated herein as comparison coupler C-2 and is represented by the formula: ##STR2## The presence of an alkoxy group in the ortho position on the phenylthio coupling-off group of coupler C-2 has provided advantageous properties. However, this coupler has not been entirely satisfactory due to formation of undesired stain in a color photographic silver halide element upon exposure and processing and because it does not provide desired image-dye density upon rapid machine processing. The coupler C-2 does not achieve full dye density, especially when the exposed color photographic element is machine processed without Lippman fine grain silver halide being present in the photographic element which can be used to effect complete conversion of the leuco-dye to image dye. It has been desirable to reduce or avoid the need for added Lippman fine grain silver halide without diminishing dye density in the processed color photographic silver halide element. It is believed that the alkoxy substituent undesirably stabilizes the leuco-dye thus preventing the completion of the dye formation process during development. This leads to loss of expected density and unpredictable results due to post-development dye formation. The prior art coupler C-2 does not therefore meet the industry needs.
Another example of a pyrazolone coupler known to the art, described in U.S. Pat. No. 4,853,319, is designated herein as comparison coupler C-3 and is represented by the formula: ##STR3## The presence of an acylamine group in the ortho position on the phenylthio coupling-off group of coupler C-3 has provided advantageous properties. This coupler does not require Lippman fine grain silver halide in order to obtain adequate dye density upon rapid machine processing. However, this type of coupler does suffer from unwanted gains in green density in unexposed areas upon standing in the dark. Another problem with couplers of this type is that in the presence of polyvalent cations such as calcium, the amount of dye formed from a given amount of exposure is reduced relative to a process with no polyvalent cations. In particular, increasing amounts of calcium ion in a seasoned process leads to unacceptable losses in dye yield with this type of coupler.
Another example of a pyrazolone coupler known to the art, described in U.S. Pat. No. 4,853,319 is designated herein as comparison coupler C-4 and is represented by the formula: ##STR4## This coupler also does not require Lippman fine grain silver halide in order to obtain adequate dye density upon rapid machine processing. However, this type of coupler also gives reduced dye yields in the presence of polyvalent cations, in particular, calcium ion.
Another type of coupler that has been considered is one having a pentachloro- substitution on the N phenyl ring (U.S. Pat. No. 4,876,182). While such materials provide advantageous properties they are not preferred because rings containing more than 3 chloro substituents present laborious and costly administrative orders relative to disposal.
It has been desired to provide a new 3-anilinopyrazolone coupler having a phenylthio coupling-off group in a color photographic silver halide element and process which is capable of forming a magenta dye image of good stability, with high dye yield based on rapid machine processing, and with reduction or omission of Lippman fine grain silver halide in the element. In addition, it has been desired to provide such a coupler which displays reduced sensitivity to polyvalent metal cations commonly found in photographic processes, specifically calcium ion. Also, it has been desired to provide such a coupler which displays excellent thermal stability in areas of no light exposure. Further, it has been desired to provide a new pyrazolone coupler which provides a magenta dye after photographic processing that has a hue suitable for optimal color reproduction and color saturation. The couplers disclosed in U.S. Pat. No. 4,853,319 that gave dyes with good hue for optimal color reproduction were generally unstable on keeping and formed undesirable stain in areas of minimum density. Finally, it has been desired to provide a new pyrazolone coupler that has high activity. High activity couplers allow for reduced material laydowns of the magenta coupler and silver halide, which in turn leads to reduced costs and improved optical quality.